W-N (Wildhaber-Novikov) gears, of the tooth profile including circular arcs centered on the pitch circle or in the neighborhood thereof, are principally intended for transmission of rotation through the medium of the helical tooth surfaces and, as is well known in the art, excel conventional involute gears in surface strength.
With such gears, it is naturally expected that the surface strength varies with the length of radius of the curcular arcs of the tooth profile and this has already been pointed out in literature. For example, in a U.S.S.R. research report, it is stated that the radius of circular arcs should preferably be larger than half the normal circular pitch.
The inventors, now taking notice of the fact that the surface strength of W-N gear teeth depends not only upon the arc radius but also upon such parameters as the tooth height and the minimum pressure angle on the arcuate regions of the tooth profile, have found that for any fixed tooth height and minimum pressure angle there exists in a practicable range an arc radius which maximizes the surface strength.